LAUSR

Abstract This paper analyzes the sedimentology and lithofacies of the lacustrine shale from the third member of the Eocene Shahejie Formation (Es3) in the Dongpu sag, Bohai bay basin, eastern China. The results show that lacustrine shale is heterogeneous in its sedimentary structure, lithology, mineralogy, lithofacies, and oil content. From the margin of the lake to its center, the depositional environment progresses from delta front to prodelta to deep water lake, and the primary sedimentary lithologies changes from interbedded mudstone and sandstone to mudstone with siltstone to mudstone with evaporite and carbonate rocks. The major deep water deposits are laminated shales. From the lake margin to the center, felsic mineral content decreases gradually, and clay mineral and pyrite content increases gradually. Felsic mineral content is the highest in the delta front shale, and clay mineral and pyrite content is highest in the deep water lake. Shale lithofacies also change with the depositional environment. The lithofacies of the delta front shale are primarily felsic-rich lithofacies: clay-rich carbonate-poor felsic shale (S-4) and a clay-rich, carbonate-poor felsic-rich mixed shale (MS-2). The lithofacies of the prodelta shale are primarily a carbonate-poor felsic-rich muddy shale (M-2), S-4, and MS-2. The lithofacies of deep water lake shales are primarily clay mineral-rich lithofacies: M-2, MS-2, and the clay-rich, carbonate-rich, felsic-rich mixed shale (MS-3). The TOC and the types of organic matter also change with the depositional environment in the Dongpu sag. The results of this study show the sedimentary structures, lithology, mineral content, lithofacies, and spatial distribution of the lacustrine shale was not only controlled by the macro depositional environment and the local depositional environment, but also controlled by the source and transport (or the sediment transport path), water depth, and accommodation space.